What is the right way to share common code across qt project?

gully

This seems fairly simple. But I somehow donot get it working.
I have 3 projects

-historical
      -historical.pro
      -main.cpp
       -mainwindow.ui

-live
      -live.pro
      -main.cpp
       -mainwindow.ui

-common
   -common.pro //these are just simple .h and .cpp files , if possible i can do away with creating a qt project
   -common.h
    -common.cpp

Now my goal

to consume files of common in both live and historical project.
To debug as usual, step into the files of common folder/project as well
Continue with life as easy as possible

Note live and historical are two completely different applications.

Here is what I have done.
Step 1:- I went into qt->right click on 'live' project->add existing files->include all the files from common pro.
Step 2: Every include statement in live or historical which referes to common i state like this

//#include"../common/common.h"

The build goes through fine but while debugging in QT Creator I am able to step-into the function. Life was just as good , when the debugger says not accessable to the value received from common functions. Wanted to know what is causing this and how can I get away with it?
I am using

Qt Creator 4.4.1
Based on Qt 5.9.2 (MSVC 2015, 32 bit)

Built on Oct 4 2017 04:12:53

From revision 6afdb8bdf9

koahnig

@gully said in What is the right way to share common code across qt project?:

//#include"../common/common.h"

This include statement is commented out. Therefore it shall have no effect in the compilation process. Possibly you are providing the information in this declaration file through some other means.

You have a couple of possible approaches.

One possibility is declaring a library with all the source files in common. The library as output has to be linked to the other applications.

When you have only few files the overhead may be too much and the direct use of the common files in the compilation process is typically faster. However, all depends on your actual plans and likings.

Anyway whatever you plan to do, you need to ensure that declaration content of common.h is only accessible in common.h. The very same physical common.h has to used in all places.

Since you are using Qt creator you can ensure and redirect the include path with http://doc.qt.io/qt-5/qmake-variable-reference.html#includepath

For instance you have

c:/SourceBase/historical
c:/SourceBase/live
c:/SourceBase/common

in all *.pro you can have a statement like

INCLUDEPATH += ../common

In your source files you can refer to the declaration file simply as

#include "common.h"

When you like to check different versions of your common source,you can simply change the INCLUDEPATH statement and redirect the include to whereever you like. Note: sometimes it is better to have a complete rebuild then.

yuvaram

Hi @gully
Adding points to @koahnig

its recommended to create a folder which is common to all the three projects(historical, live, common) i.e., A_PROJECT folder
A_PROJECT > historical, A_PROJECT > live, A_PROJECT > common

A_PROJECT folder
A_PROJECT > A_PROJECT.pro

TEMPLATE = subdirs
CONFIG += ordered
SUBDIRS = historical \
          live \
          common
historical.depends = common
live.depends = common

A_PROJECT > historical folder
A_PROJECT > historical > historical.pro

# requires more statements above 
INCLUDEPATH += ../common
# requires more statements below

A_PROJECT > live folder
A_PROJECT > live > live.pro

# requires more statements above 
INCLUDEPATH += ../common
# requires more statements below

A_PROJECT > common folder
A_PROJECT > common > common .pro

make common project as shared library & start using in other projects.

[Edit: koahnig] added code tags for .pro file snippets, because backslash was not shown for SUBDIRS

Jean_Luc

Hello,
Please and if you have 2 project and one of the 2 project is having a database where a table user existe and you want to use that database(SQLite) in the seconde project. Is it possible? If yes how. I am new in qt

SGaist

@Jean_Luc hi and welcome to devnet,

Yes. Write the code required in that project for that.
The fact that it uses a database is no different than if it would implement some network related stuff.

VRonin

@SGaist said in What is the right way to share common code across qt project?:

The fact that it uses a database is no different than if it would implement some network related stuff.

Kinda... Sqlite is not a full DB server. See https://stackoverflow.com/questions/10325683/can-i-read-and-write-to-a-sqlite-database-concurrently-from-multiple-connections for the restrictions

SGaist

@VRonin Indeed but I was thinking code wise and may have misunderstood the OP question.

If the question is whether you can access the same SQLite database file from two different applications, then yes, I completely agree with your post.

My point was that having SQLite related logic in a shared library that you can reuse in different applications is fine.